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Phylum Mollusca

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Visceral mass and nervous system become twisted 90-180 during ... Anemone Sea Slug. Gastropods. 15. Subclass comparisons. Different from prosobranchia: ... – PowerPoint PPT presentation

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Title: Phylum Mollusca


1
Phylum Mollusca
  • Class Gastropoda

2
Class Gastropoda
  • Defining characteristics
  • Visceral mass and nervous system become twisted
    90-180 during embryonic development
  • Proteinaceous shield on the foot (operculum)

3
Gastropod Morphology and Movement
  • The typical snail consists of a visceral mass,
    which sits atop a muscular foot
  • The visceral mass is protected by a univalve
    shell that is coiled

4
Dextral and Sinistral Coiling
  • The shell is usually carried on the left side of
    the body and coils to the right (dextral)
  • Few species are sinistral
  • Shell coils to the left (lightning whelk)

5
Torsion
6
Gastropod Movement
  • Most move via cilia located on the ventral
    surface of the foot or through pedal waves

7
Subclass Prosobranchia
  • Defining characteristic
  • Mantle cavity generally anterior due to torsion
  • Usually have protective shells
  • Includes most marine gastropods

Oyster Drills
8
Prosobranchia External Anatomy
9
Prosobranchia Anatomy
  • Molluscan gill
  • Ctenidium, consists of a series of flattened,
    triangular sheets
  • Water is drawn into the animal by gill cilia
  • Osphradium

10
Reproduction
  • Life begins as a trochophore larvae which then
    develops into a veliger larvae
  • The veliger is where most of the organ systems
    develop
  • During development the process of torsion begins

11
Local Representatives
  • Banded Tulip (Fasciolaria tulipa)
  • Knobbed Whelk (Busycon carica)

True Banded Tulip
12
Subclass Opisthobranchia
  • Defining characteristic
  • Mantle cavity located posteriorly due to
    detorsion
  • Sea slugs and sea hares

13
Gas exchange and defense
14
Nudibranchs, Sea slugs, Sea hares
  • A radula and foot for creeping is usually present
    (sea slugs)
  • Some have parapodia used for swimming
  • Well developed head and sensory tentacles

Anemone Sea Slug
15
Lemon Nudibranch
Nudibranchs have no shell or mantle cavity Lack
gills, instead have respiratory projections on
the dorsal surface
16
Subclass comparisons
  • Different from prosobranchia
  • Reduction or loss of the shell and operculum
  • Limited torsion
  • Reduction or loss of the mantle cavity
  • Reduction or loss of ctenida
  • Many have evolved different respiratory
    structures which are unrelated to ctenidia

17
Local species
  • Sooty sea hare (Aplysia brasiliana)
  • Have large swimming parapodia and a greatly
    reduced shell on the back
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